Generally, a damper device is provided, for example, on a power transmission path between an engine and a clutch, so that the damper device absorbs (reduces) torque fluctuation generated by the engine and a transmission apparatus. More specifically, the damper device generates torsion when the torque fluctuation occurs in order to absorb (reduce) the torque fluctuation by a spring force generated by a coil spring, a hysteresis torque generated by a friction material, and the like. A shock is likely to generate when the engine starts in a case where the damper device is configured so as to generate a small hysteresis torque. Therefore, the damper device is preferably configured so as to generate a relatively great hysteresis torque. On the other hand, in a case where the damper device is configured so as to generate a great hysteresis torque, the damper device is less likely to generate the torsion, thereby generating noise such as booming noise, gear grinding noise and the like. In order to reduce the noise, for example, a viscous fluid torsional vibration damping device, which is disclosed in JP H7-27172A and which includes a damper device configured so that a hysteresis torque is generated variably in response to a torsional vibration, is proposed.
In the viscous fluid torsional vibration damping device disclosed in JP H7-27172A, a hysteresis torque is generated by a hydraulic choke of a viscous damper mechanism. Furthermore, the viscous fluid torsional vibration damping device disclosed in JP H7-27172A includes a slide stopper having a projection, which inwardly protrudes in a radial direction of the viscous fluid torsional vibration damping device, and a driven member having a recessed portion at a radially outer end portion thereof. When the torsional angle between the slide stopper and the driven member becomes great, an end portion of the projection of the slide stopper in the radial direction contacts a circumferential end portion of the recessed portion of the driven member, thereby pushing the slide stopper in a radially outer side thereof. Accordingly, an outer circumferential surface of the slide stopper is pressed against an inner circumferential surface of a rim portion. As a result, a resistance force is generated between the slide stopper and the rim portion by friction generated therebetween.
In the viscous fluid torsional vibration damping device disclosed in JP H7-27172A, the projection of the slide stopper separates a space formed by the recessed portion of the driven member into a first sub-chamber and a second sub-chamber in a rotational direction, thereby forming a choke between the end portion of the projection of the slide stopper and a bottom surface of the recessed portion of the driven member so as to allow a viscous fluid to flow between the first and second sub-chambers. Accordingly, the projection of the slide stopper serves as a piston, according to JP H7-27172A. In order to use the projection of the slide stopper as the piston, surfaces of the slide stopper in an axial direction thereof need to closely contact a first flywheel and a drive plate, respectively. Further, an inner circumferential end surface of the projection of the slide stopper in the radial direction thereof needs to closely contact the first flywheel. The slide stopper is formed so that contact surfaces thereof in the axial direction and the radial direction are set to be relatively large. Therefore, relatively great friction resistance is likely to be generated between the slide stopper on the one hand and the first flywheel and the drive plate on the other hand, which may result in generating a friction resistance between the slide stopper and the rim portion. However, generating relatively great friction resistance between the first flywheel and the drive plate, and between the slide stopper and the rim portion may deteriorate damping function of the viscous fluid torsional vibration damping device. Furthermore, for example, in a case where thermal expansion occurs at the slide stopper, the slide stopper on the one hand and the first flywheel and the drive plate on the other hand may not closely contact, thereby deteriorating viscous damping function of the viscous fluid torsional vibration damping device. Moreover, occurrence of the friction resistance between the slide stopper and the rim portion may also deteriorate the viscous damping function. In order to maintain the viscous damping function of the viscous fluid torsional vibration damping device, clearances need to be carefully controlled, which may result in increasing manufacturing costs.
According to the viscous fluid torsional vibration damping device disclosed in JP H7-27172A, the projection of the slide stopper inwardly protrudes in the radial direction thereof, so that the slide stopper contacts the rim portion at radially outer surfaces of the slide stopper. However, because of the configuration of the slide stopper, the viscous fluid torsional vibration damping device may easily be influenced by centrifugal force, thereby deteriorating the damping function in view of the occurrence of the friction force.
Further, according to the viscous fluid torsional vibration damping device disclosed in JP H7-27172A, because plural slide stoppers are separately provided in a circumferential direction of the viscous fluid torsional vibration damping device, misalignment may occur at each slide stopper, thereby deteriorating the damping function of the viscous fluid torsional vibration damping device in view of the occurrence of the friction force.
In a case where the slide stoppers, which are separately provided at the viscous fluid torsional vibration damping device in the circumferential direction thereof, are set so that angles of inclined contact surfaces of the slide stoppers to be the same, a shock generated when the inclined contact surfaces contact each other is not likely to be dispersed, which may result in increasing noise generated by the device when the inclined surfaces contact each other.
According to the viscous fluid torsional vibration damping device disclosed in JP H7-27172A, the slide stopper is configured so as to contact the rim portion at the radially outer surface. However, in a case where the radially outer surface of the slide stopper is formed to have a flat surface, friction dust may be generated because of the friction generated between the slide stopper and the rim portion, which may deteriorate the occurrence of the friction force because of the friction dust.
According to the viscous fluid torsional vibration damping device disclosed in JP F7-27172A, the projection of the slide stopper inwardly protrude in the radial direction thereof, so that the slide stopper contacts the rim portion at the radially outer surface of the slide stopper. However, the above-described configuration of the slide stopper may deteriorate a load balance, which may result in insufficiency of the friction force.
A need thus exists to provide a damper device which is not susceptible to the drawback mentioned above.